The present invention relates to a field of a molding machine and, in particular, concerned to a system for feeding portions of material to a plastic-injection molding machine.
Several weight feeding apparatus and systems are known. These apparatus and systems are for feeding a large quantity of material. When a small quantity is needed, e.g., coloring material, in a producing system, volume methods are used to achieve the needed weight. Volume methods are used for feeding small quantities because of the difficulty of weighing a few grams in the production area, which is very noisy and shaky.
Volume feeding methods, which are used to achieve weight feeding, have some disadvantages. The specific gravity of a material can be changed e.g., in a new production batch, and therefore a new scaling is needed. The volume-weight scaling is a long process and requires skilled workers. Moreover, since the fed volume cannot be controlled the volume-feeding method assumes that the feeder dispenses equal portions permanently and therefore ignores the material streaming problems.
Feeding hopper usually has an outlet to feed the material. Part of the material, the material in the shaft that is perpendicular to the outlet, does not press on the hopper. This xe2x80x9coutlet-shaftxe2x80x9d causes an error in the hopper weighing since the material in the outlet-shaft or at least part of this material is not weighed. Load cells are calibrated when weighing such hoppers.
There is therefore a recognized need for, and it would be highly advantageous to have, a system for feeding portions of material to an injection-molding machine with the ability to accurately weigh feeding of small quantities of material.
The present invention is a system for feeding portions of material to an injection-molding machine with the ability to accurately weigh feeding of small quantities of material.
According to the teachings of the present invention there is provided, a system for feeding portions of material to an injection molding-machine including (a) a feeding means; (b) a container, with a fill opening and an outlet, and the container is installed with the feeding means; (c) a material hopper, with a fill opening and an outlet, and the material hopper is located inside the container; (d) a load cell that is coupled to the material hopper, and (e) a controller operative for: (i) calculating the weight of fed material, using the load cell and loss-in-weight method, and (ii) controlling the feeding means.
According to further features in the described preferred embodiments, the material hopper of the system has a funnel shaped lower part and an upper part and wherein the upper part has the same cross-section-area in each vertical level. The upper part of the material hopper can have inclined parallel-walls.
According to further features in the described preferred embodiments, the controller of the system is further operative for command the feeding means to dispense at least one portion of material from the material hopper, wherein each portion is dispensed in a given time and for a given interval of time in order to dispense portions with a predetermined weight.
According to further features in the described preferred embodiments, the controller is further operative for it calculates the weight of the dispensed portion by (1) dispensing a number of portions; (2) calculating the weight of the number of portions, using loss-in-weight method, and (3) dividing the weight of the number of portions to the number of the portions.
According to further features in the described preferred embodiments, the feeding means is a screw feeder and the controller is further operative for adjusting the weight of the further portion by increasing or decreasing the spin speed of the screw feeder, if the weight of the portion differs from the predetermined weight.
According to further features in the described preferred embodiments, the outlet of the material hopper is shifted and elevated from the outlet of the container.
According to yet another aspect of the present invention there is provided a material hopper for accurate weighing including (a) a funnel shaped lower part with outlet, and (b) a parallel or cylinder walls upper part wherein the walls can be inclined.
According to yet another aspect of the present invention there is provided a method of accurate weighing of a fed portion including (a) storing the material in a material hopper that it""s upper part is an inclined cylinder or an inclined parallel walls; (b) feeding a predetermined number of portions; (c) calculating the weight of the number of portions, using loss-in-weight of the material hopper using a load cell, and (d) calculating the weight of each portion of the number of portions by dividing the weight of the number of portions to the number of the number of portions. The predetermined number of portions can be calculating by dividing the sensitivity of the load cell to the estimated weight of the fed portion.
The present invention successfully addresses the shortcomings of the existing technologies by providing a system for feeding portions of material to an injection-molding machine with the ability to accurately weigh feeding of small quantities of material.